01 - Preheat oven to 350°F (180°C). Grease a medium-sized baking dish with nonstick spray or butter.
02 - Steam or blanch broccoli florets and carrot slices for 3 to 4 minutes until just tender, then drain thoroughly and set aside.
03 - In a medium saucepan over medium heat, melt 2 tablespoons butter. Whisk in the flour and cook for 1 minute, stirring to form a smooth roux.
04 - Gradually whisk in 1 cup milk until the mixture thickens and is smooth. Remove from heat and add shredded cheddar cheese, garlic powder, onion powder, salt, and pepper, stirring until cheese is fully melted and sauce is creamy.
05 - Fold the blanched broccoli and carrots into the cheese sauce gently, ensuring even coating. Transfer the mixture to the prepared baking dish.
06 - In a mixing bowl, combine panko breadcrumbs, melted butter, and Parmesan cheese if using. Sprinkle the mixture evenly over the vegetables in the baking dish.
07 - Bake for 25 to 30 minutes, or until the top is golden brown and the filling is bubbling. Let rest for 5 minutes before serving.